Decommissioning and dismantling nuclear power plants
Due to its decision to phase out nuclear energy, adopted in 2000, Germany has more experience and more projects relating to the dismantling of nuclear facilities than most other countries around the world.
Currently, 22 nuclear reactor units are in various stages of decommissioning in Germany: Grafenrheinfeld, Biblis A and B, Isar 1, Gundremmingen B, Philippsburg 1 and 2, Neckarwestheim 1, Unterweser, Brunsbüttel, Mülheim-Kärlich, Stade, Obrigheim, Lingen, Hamm-Uentrop, Würgassen, and two nuclear power plants constructed in the former GDR: Rheinsberg, which has one reactor unit, and Greifswald, which has five. A dismantling licence has yet to be granted for Krümmel NPP. Applications have already been submitted for the decommissioning and dismantling of Neckarwestheim 2, Isar 2, Gundremmingen C, Brokdorf, Grohnde and Emsland, which are scheduled to be taken offline within the next few years.
In the past, an alternative to immediate dismantling was “safe enclosure” for a period of around three decades, followed by dismantling. This was based on the assumption that allowing time for the radioactivity to decay would reduce the volume of radioactive waste produced. In practice, however, it has been demonstrated that employees with operational experience and knowledge of the plant and its history have a very important role to play in decommissioning. A safe enclosure strategy is in operation solely at Lingen nuclear power plant and the thorium high-temperature reactor in Hamm-Uentrop.
Following the amendment of the German Atomic Energy Act in 2017, Germany now grants licences solely for immediate dismantling, as this approach has proved to be advisable for reasons of safety, management and economic efficiency. The goal of dismantling is to effect the release of the nuclear installation from regulatory control. The Oeko-Institut monitors all these processes in its capacity as an external consultant.
Preparation and licensing of immediate dismantling
Once it has ceased operation, a nuclear power plant enters the post-operational phase. This lasts until the dismantling licence has been granted and activated. During this period, the remaining fuel elements are removed from the reactor pressure vessel and placed in the cooling pond. Spent fuel is loaded into transport and storage containers and taken to an interim storage facility. The aim is to remove all the nuclear fuel from the power plant before decommissioning begins.
Once all the fuel elements have been removed from the pond, less stringent safety requirements apply. The storage ponds can be used for disassembly operations and dismantling can commence with no restrictions.
Post-operation
During the operation of a nuclear power plant, technical components and parts of buildings become more radioactive with increasing exposure to nuclear fuel. This applies, for example, to the reactor pressure vessel and its internal metal components, which are exposed to neutron radiation, a highly penetrating form of radiation; they thus become radioactive themselves. Some of the pipes used in the coolant circuit may also be contaminated with radioactive substances that settle in them.
Another key task during post-operation is therefore to categorise all the rooms and plant components according to the expected level of radioactivity or contamination. A good knowledge of the plant and its operating history are important, for example, in order to identify and conduct more precise measuring in potentially contaminated areas. This detailed radiological characterisation is essential for optimising the sequencing of the dismantling process, adopting the necessary radiation protection measures and estimating waste volumes.
Other tasks include the emptying and decontamination of pipes and the dismantling of conventional areas of the facility that are no longer needed. Enough space must be made available for the processing and storage of radioactive residues produced during subsequent dismantling of components. In some cases, this may mean setting up residue processing centres in existing buildings or constructing new facilities on-site. At almost all the nuclear power plants, new buildings are constructed for interim storage of low- and intermediate-level radioactive waste.
Separate from the work undertaken during the post-operational phase, the required technical documentation must be submitted to the competent supervisory authority at the Land (state) level for review. This process must include the following:
Decommissioning and dismantling: the process in detail
1. The decommissioning and dismantling licence
A decommissioning and dismantling licence is the starting point for numerous parallel activities. Transport systems must be established, including lifts, sluices, buffer storage areas and space for cutting equipment. As a rule, dismantling starts in areas with low contamination and then continues in areas with higher levels of radioactivity and contamination.
In general, a two-stage approach is applied. During Phase I, the highly radioactive components are removed from the reactor pressure vessel (RPV), along with large items of equipment such as the steam generator, the pressuriser, cooling water pumps and primary coolant circuit. Components that are large, heavy or significant in terms of radiation protection are disassembled and sent for residue processing.
The removal of the fuel elements and reactor pressure vessel’s internal components greatly reduces the level of radioactivity in the reactor building. In Phase II, the reactor pressure vessel is dismantled, along with the biological shield and the spent fuel pond.
2. Waste strategy and processing
A detailed radiological characterisation enables the residues produced in dismantling to be categorised as: (1) radioactive waste, (2) waste for nuclear recycling, (3) substances that may be granted clearance for specific purposes, (4) substances that are suitable for unrestricted clearance, and (5) uncontaminated plant components, buildings and parts of the site outside the controlled area. The Oeko-Institut provides advice primarily on clearance for specific purposes and unrestricted clearance.
According to preliminary data provided in the safety reports, a 1300 MW reactor produces between 3,000 and 5,000 tonnes of radioactive waste. Taking the Unterweser NPP as an example, it is currently assumed that this is 2 per cent of the material from the controlled area, while 6 per cent is suitable for clearance for specific purposes and 92 per cent can be granted unrestricted clearance. The actual figures will not be confirmed until dismantling is complete.
3. The Oeko-Institut’s role
By far the majority of nuclear power plant components are buildings and installations that were never contaminated with radioactivity, such as the staff facilities, the pump houses for river water and the emergency power generator buildings. They are located outside the controlled area and the review of the operating history confirms that they were never contaminated. Clearance is granted on the basis of plausibility assessments and sample measurements.
By contrast, all the components from the controlled area must undergo the formal clearance procedure stipulated in radiation protection legislation and the German Atomic Energy Act (Atomgesetz – AtG). The individual components are disassembled and decontaminated – which involves cleaning them to remove radioactive material – and then undergo clearance measurement. Clearance is granted only if the materials are verified by experts, in accordance with the procedure stipulated by law, as falling below the specified permissible clearance limits; this guarantees that they pose no risk to public health. The researchers at the Oeko-Institut advise the German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU) on the statutory provisions. They also advise the state (Land) authorities on supervising the implementation of these rules.
Securing public acceptance for this process, whose purpose is to ensure compliance with the highest radiation protection standards, is often challenging, especially as regards restricted clearance of materials that are destined for landfill or incineration as hazardous waste. At this interface between operators, the authorities and the general public, the Oeko-Institut endeavours to achieve transparency, raise awareness and develop potential solutions that are acceptable to all sides.
4. Interim storage: who’s responsible?
In principle, responsibility for the disposal of spent fuel elements, high-level radioactive waste from reprocessing, and low- and intermediate-level radioactive waste from NPP operation lies with the waste producers, i.e. the plant operators and energy supply companies. Under the Act to regulate the transition of nuclear power plant operators’ financial and operational responsibilities in respect of radioactive waste disposal (Disposal Transition Act (Entsorgungsübergangsgesetz – EntsorgÜG)) of 16 June 2017, these waste streams are transferred to the BGZ Gesellschaft für Zwischenlagerung mbH, which has been commissioned by the Federal Government to operate interim storage of radioactive waste once it has been properly conditioned. Handover takes place at the interim storage facilities, almost all of which are now owned by the Federal Government. The operators have already paid 23.75 billion euros into a fund for this specific purpose, thereby transferring the responsibility for radioactive waste disposal to the Federal Government.
Once the Konrad repository near Wolfenbüttel is operational, all low- and intermediate-level radioactive waste will be permanently stored there.
5. The purpose of decommissioning and demolition
Most decommissioning applications state that the purpose of decommissioning is to enable the nuclear facility to be released from regulatory control. However, they emphasise that the Demolition of released buildings can be conducted with conventional law. As yet, none of the reactor buildings from the large power reactors have been demolished. Both the on-site interim storage facilities for spent fuel elements and the interim storage facilities for low- and intermediate-level radioactive waste will continue to exist after the release of the other parts of the plant, so clearance of the NPP sites is likely to take several decades.
Yet to be identified: a final storage site
Where should the spent fuel elements and other high-level radioactive waste be stored? This issue is still unresolved. The process of selecting a repository site and furnishing proof of its long-term safety is still ongoing. The 2017 Site Selection Act sets out in detail the procedure for identifying a suitable repository site. Other essential steps include securing public acceptance and obtaining a repository licence.
Decommissioning of the Active Storage Facility for Residuals at the site of the Rheinsberg NPP
For 23 years – since 1997 – Oeko-Institut scientists have been assisting with the dismantling of the former storage facility for radioactive waste at the Rheinsberg nuclear power plant. During its operational life, its buildings were heavily contaminated by radioactive liquids as a result of accidents that occurred in the 1970s and 1980s. This also resulted in radioactive contamination of soil and groundwater.
The most pressing concern for the Oeko-Institut in 1997 was therefore to urge immediate dismantling to prevent further radioactive contamination of soil and groundwater.
Since then, the Oeko-Institut has been supporting the dismantling process by providing external consultancy services. It has also identified the tasks of greatest importance for soil and groundwater protection. This includes developing strategies to ensure compliance with stringent radiation protection objectives. Implementation of the strategies is continuously monitored. To that end, the Oeko-Institut’s scientists liaise closely with the state of Brandenburg’s nuclear regulatory authority. They review the applications submitted by the operator on an ongoing basis, evaluate the results and produce technical advice on methodological issues.
A key concern in the context of radiation protection in the course of dismantling operations is to prevent radioactive substances entering the soil and groundwater. However, large quantities of radioactive isotopes have already entered the environment. The Oeko-Institut is therefore developing comprehensive clean-up solutions with the aim of ensuring that at some point in the future, the site will no longer pose a risk to human health and the environment.